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Jannik Beyerstedt 2026-07-31 15:51:10 +02:00
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src/tx/mod.rs Normal file
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//! V2X Transmission Utilities
use alloc::vec::Vec;
use c_its_parser::gn as geonetworking;
pub mod gn;
/// Interface for ITS Payloads inside a Geonetworking header
pub trait GnItsPayload {
// common GN parameters
const LIFETIME_MILLIS: u32 = 60_000; // itsGnDefaultPacketLifetime is 60 seconds according to ETSI EN 302 636-4-1 V1.4.1
// ---------------------------------------------
// methods to build a GN packet with ITS payload
// ---------------------------------------------
/// Builds the [`geonetworking::en302636_4_1::ExtendedHeader`] and additional information for the ITS message
///
/// Output:
/// - Extended header
/// - Area type (when using GAC or GBC)
/// - hop limit
///
/// Note: Make sure to increase the sequence number on multi-hop packets.
///
/// # Errors
/// Returns a human-readable error description if values are out of range
fn make_eh(
&self,
address: [u8; 6],
own_position: &crate::PosVel,
time: chrono::DateTime<chrono::Utc>,
seq_no: &mut u16,
) -> Result<
(
geonetworking::en302636_4_1::ExtendedHeader,
Option<geonetworking::en302636_4_1::AreaType>,
u8,
),
alloc::string::String,
>;
/// Creates the ITS payload (without BTP header)
///
/// # Errors
/// Returns a human-readable error description if values are out of range
fn make_payload(
&self,
) -> Result<(Vec<u8>, c_its_parser::standards::extensions::ItsMessageId), alloc::string::String>;
// ---------------------------------------------
// common methods (with implementation)
// ---------------------------------------------
/// Encodes the GN packet
///
/// # Errors
/// Returns a human-readable error description if values are out of range
fn encode_packet(
&self,
address: [u8; 6],
own_position: &crate::PosVel,
time: chrono::DateTime<chrono::Utc>,
is_mobile: bool,
seq_no: &mut u16,
) -> Result<Vec<u8>, alloc::string::String> {
use geonetworking::Encode as _;
// Build payload (including BTP header)
let (mut its_payload, msg_type) = self.make_payload()?;
let mut payload = make_btp_b(msg_type).encode()?;
payload.append(&mut its_payload);
#[allow(clippy::cast_possible_truncation)]
let payload_length = (payload.len()) as u16;
// get extended header (depending on message type and sometimes content as well)
let (eh, area_type, maximum_hop_limit) =
self.make_eh(address, own_position, time, seq_no)?;
// Build GN headers
let traffic_class = geonetworking::en302636_4_1::TrafficClass::try_new(
false,
false,
make_traffic_class(msg_type),
)
.map_err(|err| alloc::format!("Failed to create TrafficClass: {err:?}"))?;
let common = geonetworking::en302636_4_1::CommonHeader::from_values(
geonetworking::en302636_4_1::NextAfterCommon::BTPB,
geonetworking::en302636_4_1::HeaderType::new_from(&eh, area_type)?,
traffic_class,
is_mobile,
payload_length,
maximum_hop_limit,
);
let remaining_hop_limit = maximum_hop_limit;
let basic = geonetworking::en302636_4_1::BasicHeader::try_new(
1,
geonetworking::en302636_4_1::NextAfterBasic::CommonHeader,
geonetworking::en302636_4_1::Lifetime::from_milliseconds(Self::LIFETIME_MILLIS),
remaining_hop_limit,
)
.map_err(|err| alloc::format!("Failed to create BasicHeader: {err}"))?;
// Assemble and encode packet
let packet = geonetworking::Packet::Unsecured {
basic,
common,
extended: Some(eh),
payload: &payload,
};
packet
.encode_to_vec()
.map_err(|err| alloc::format!("Failed to encode GN packet: {err:?}"))
}
}
/// Creates a BTP-B header based on the ITS message ID (message type)
///
/// Port numbers and destination port info according to ETSI TS 103 248
fn make_btp_b(
msg_type: c_its_parser::standards::extensions::ItsMessageId,
) -> c_its_parser::transport::TransportHeader {
let (destination_port, destination_port_info) = match msg_type {
c_its_parser::standards::extensions::ItsMessageId::Denm => (2002, 0),
c_its_parser::standards::extensions::ItsMessageId::Cam => (2001, 0),
c_its_parser::standards::extensions::ItsMessageId::Mapem => (2003, 0),
c_its_parser::standards::extensions::ItsMessageId::Spatem => (2004, 0),
c_its_parser::standards::extensions::ItsMessageId::Saem => (2005, 0),
c_its_parser::standards::extensions::ItsMessageId::Ivim => (2006, 0),
c_its_parser::standards::extensions::ItsMessageId::Srem => (2007, 0),
c_its_parser::standards::extensions::ItsMessageId::Ssem => (2008, 0),
c_its_parser::standards::extensions::ItsMessageId::Cpm => (2009, 0),
c_its_parser::standards::extensions::ItsMessageId::Poi => (2010, 0),
c_its_parser::standards::extensions::ItsMessageId::EvRsr => (2012, 0),
c_its_parser::standards::extensions::ItsMessageId::Rtcmem => (2013, 0),
_ => (0, 0), // no information found for the subsequent types
};
c_its_parser::transport::TransportHeader::BtpB(c_its_parser::transport::BasicTransportBHeader {
destination_port,
destination_port_info,
})
}
/// Creates a traffic class ID based on the ITS message ID (message type)
fn make_traffic_class(msg_type: c_its_parser::standards::extensions::ItsMessageId) -> u8 {
#[allow(clippy::match_same_arms)]
match msg_type {
c_its_parser::standards::extensions::ItsMessageId::Denm => 1,
c_its_parser::standards::extensions::ItsMessageId::Cam => 2,
c_its_parser::standards::extensions::ItsMessageId::Mapem => 3, // from C-Roads RS_RSP_063(1)
c_its_parser::standards::extensions::ItsMessageId::Spatem => 3, // from C-Roads RS_RSP_063(1)
c_its_parser::standards::extensions::ItsMessageId::Ivim => 3, // from C-Roads RS_RSP_063(1)
c_its_parser::standards::extensions::ItsMessageId::Srem => 2, // from C-Roads RS_RSP_063(1)
c_its_parser::standards::extensions::ItsMessageId::Ssem => 2, // from C-Roads RS_RSP_063(1)
c_its_parser::standards::extensions::ItsMessageId::Rtcmem => 3, // CSP_MaxPrio=252 -> 3
_ => 3, // fall-back to lowest priority
}
}